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Piedmont 03-20-2009 02:22 PM

Understanding sensors for data logging
 
I have several questions about sensors if anyone can help answer one or all :yes:!

1.) What is the difference between a split-core sensor and a solid core sensor (specifically trying to monitor AC amps). What equipment/situations would you choose one vs. the other and vice versa?

2.) What is a state sensor? It says it operates on contact closures... what are examples of items utilizing contact closures?

3.) Why doesn't it appear a split/solid core AC amp sensor can monitor motors? It looks like if I wish to track when a motor turns on/off I need a special magnetic field sensing sensor attached right to the motor (so it knows by the magnetic field when it's on/off) or the data logger has to be able to detect states and requires a special selective threshold AC amp sensor, as a regular amp sensor won't do apparantly. What's special about motors and why can't a regular split/solid core AC sensor work on them?

Thanks for any help, I know these are rather technical.

skizsam 03-20-2009 04:26 PM

Quote:

Originally Posted by Piedmont (Post 247432)
I have several questions about sensors if anyone can help answer one or all :yes:!

1.) What is the difference between a split-core sensor and a solid core sensor (specifically trying to monitor AC amps). What equipment/situations would you choose one vs. the other and vice versa?

2.) What is a state sensor? It says it operates on contact closures... what are examples of items utilizing contact closures?

3.) Why doesn't it appear a split/solid core AC amp sensor can monitor motors? It looks like if I wish to track when a motor turns on/off I need a special magnetic field sensing sensor attached right to the motor (so it knows by the magnetic field when it's on/off) or the data logger has to be able to detect states and requires a special selective threshold AC amp sensor, as a regular amp sensor won't do apparantly. What's special about motors and why can't a regular split/solid core AC sensor work on them?

Thanks for any help, I know these are rather technical.

Not sure if I'll directly answer your questiosn but I'll chime in since I'm an electrical engineer:

Amps are amps and it doesn't matter what type of devise is drawing amps (motor, power supply, washer, dryer, fridge, etc) So in theory,All you need is a good meter that can capture the timeframe/cycle of what your looking for.

As for split/solid, I'm not 100% sure but I think a split core literally splits so you can put the the core around the wire without cutting the wire. If you had a solid core sensor, then you would need to cut the wire to apply the sensor. It just depends on your applications and how things are installed. Obviously, a split core is easy to install if your motor/system is already hardwired.

As for datalogging, I'm very familiar with Dranetz-BMI, and their dataloggers can measure any motor's amps with the respect CT(split or solid).

If I didn't answer your question, then I'll need more detail on what your trying to do.

wirenut1110 03-20-2009 05:37 PM

Quote:

Originally Posted by Piedmont (Post 247432)

2.) What is a state sensor? It says it operates on contact closures... what are examples of items utilizing contact closures?

My guess would be just a set of contacts, whether they be on your current sensing relay, relay, or auxiliary contacts on a contactor/starter. Even if it's just dry contacts.

As far as examples, you would use contacts to make something else happen or not happen at the same time your motor starts. Like if you're data logger needs dry contacts to start recording data, you have a set of NO contacts on the starter and when the motor started, so would the data logger.

I agree that you would need a special current sensor for a motor other than being the starting current being in the range of the sensor.

hayewe farm 03-20-2009 05:50 PM

Quote:

Originally Posted by Piedmont (Post 247432)
I have several questions about sensors if anyone can help answer one or all :yes:!

1.) What is the difference between a split-core sensor and a solid core sensor (specifically trying to monitor AC amps). What equipment/situations would you choose one vs. the other and vice versa? I can't answer this because to be quite frank I don't remember.

2.) What is a state sensor? It says it operates on contact closures... what are examples of items utilizing contact closures? When you attach a continuity tester to a switch and you open and close the switch you are sensing the state of the switch open or closed. When you attach a test light between a hot and neutral lead you are sensing the state power on or power off. Sensing the state only supplies the information open or closed or power on or off no other information. As an example of utilizing contact closure would be the first example I gave with the switch Or you hook a relay to the output of a pressure switch when the pressure switch closes and supplies power to a pump it would also pull the relay up. By monitoring the continuity of a set of contacts on the relay you would be utilizing contact closure.

3.) Why doesn't it appear a split/solid core AC amp sensor can monitor motors? It looks like if I wish to track when a motor turns on/off I need a special magnetic field sensing sensor attached right to the motor (so it knows by the magnetic field when it's on/off) or the data logger has to be able to detect states and requires a special selective threshold AC amp sensor, as a regular amp sensor won't do apparantly. What's special about motors and why can't a regular split/solid core AC sensor work on them? An AC amp sensor works by measuring the magnetic field established by current flow in a conductor. They can be used for motors but the power feed, hot and neutral, must be separated so you can attach to only one lead because the current flow in the hot and neutral is in opposite directions and produce magnetic fields in opposite direction that cancel each other out.

Thanks for any help, I know these are rather technical.

I hope that helps answer some of your question.
Jack

theatretch85 03-20-2009 06:40 PM

Quote:

Originally Posted by Piedmont (Post 247432)
I have several questions about sensors if anyone can help answer one or all :yes:!

1.) What is the difference between a split-core sensor and a solid core sensor (specifically trying to monitor AC amps). What equipment/situations would you choose one vs. the other and vice versa?

2.) What is a state sensor? It says it operates on contact closures... what are examples of items utilizing contact closures?

3.) Why doesn't it appear a split/solid core AC amp sensor can monitor motors? It looks like if I wish to track when a motor turns on/off I need a special magnetic field sensing sensor attached right to the motor (so it knows by the magnetic field when it's on/off) or the data logger has to be able to detect states and requires a special selective threshold AC amp sensor, as a regular amp sensor won't do apparantly. What's special about motors and why can't a regular split/solid core AC sensor work on them?

Thanks for any help, I know these are rather technical.

1. Split core simply means you can install it with out disconnecting or cutting the wire, most specifically the hot conductor. The solid core you would need to disconnect the wire you are monitoring first and feed it through. Some examples of usage, Split Core is useful on the Mains where disconnecting would be either difficult or impossible (depending on if there is an upstream disconnect). Solid core can probably be used just about everywhere else, just so long as you can disconnect the wire and pass it through the CT then reconnect the wire.

2. hayewe farm covered this one pretty well. Some additional thoughts, you could use a door switch to sense when a door is open or closed (like in a security system) though this would be just for data logging.

3. This I am not sure on, however you can only install the CT's on the hot conductor, it does not matter what the load is motor or otherwise. Try putting a CT around an extension cord and turn on a heavy load, it won't detect anything because you need to isolate the hot wire to place the CT around it. I would think you could monitor a motor load, though it may not be as accurate or precise as the magnetic sensor would be.

Yoyizit 03-20-2009 07:33 PM

The split core somehow compensates for the increased reluctance of the air gap. The other has a uniform flux density in the magnetic path, so I guess the relationship between mag. flux sensed and output V or I is more nearly linear.


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